Rheostat construction



' Dec. 16, 1941. A. A. FOLEY ET AL RHEOSTAT CONSTRUCTION Filed Oct. 7, 1939 n ma SAM U R v N w Wm met 0w AEM Y B. M

Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE? BHEOSTAT CONSTRUCTION Andrew A. Foley, Camden, N. 1., and Emil Reisman, Aidan, Pa., assig'nors to International Resistance Company; Philadelphia, Pa., a corporation of Delaware Application October 7, 1939, Serial No. 298,412

7 Claims. (01. 201-55) This invention relates to resistor construction and more particularly to rheostat especially adapted for high capacity operation.

One of the objects of this invention is to provide a rheostat which will be simple, practical and thoroughly durable in operation. Another object is to provide a rheostat of the above characterwhich may bemanuiactured from inexpensive materials at low labor cost. Another object is to provide a rheostat of the above character which despite a small and inexpensive construction is capable of enduring without danger or damage relatively high current capacities. Another object is to provide a rheostat in which heat generated by the resistance element while operating is rapidly and eillciently dissipated. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements,

[ and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the various possible embodiments of this invention,

Figure 1 is a plan view of the open side of our rheostat;

Figure 2 is a vertical sectional view taken along the line 2-2 of Figure 1;

Figure 3 is a perspective view of the casing of our rheostat:

Figure 4 is a perspective view of the resistance element as assembled preparatory to installation inthe casingshowninFlgureii; and

Figure 5 is an enlarged vertical section I through the resistance element shown in Figcy,to generate large amountsof heat not only damaging to the rheostat construction but also toother electrical parts which by necessity must be located closely adjacent thereto. The operation of such rheostats at very high temperatures is not onlydamaging to the apparatus but inconvenience where space factors are important.

Furthermore, where the situation has necessitated the use of small rheostats to take care of relatively high currents, depreciation and resultant replacements have been annoying factors. One of the objects of this invention is to provide a rheostat construction in which the above-mentioned dimculties as, well as many others are successfully obviated.

Referring now to Figure 1, there is shown a cup-shaped metallic casing generally indicated at I ll with a resistance element generally indicated at ll concentrically mounted therein. A

contactor generally indicated at I! is rotatably mounted'in the casing to slidably engage the resistance element H. As best shown in Figure 2, the resistance element II is cylindrical in shape and adjacent the vertical wall of the housing It;

thus the element is in heat exchange relationship with the casing so that heat generated in the element may pass quickly to the casing and thus be dissipated in the atmosphere.

Casing iii, preferably a cast metal such as aluminum, is substantially cupshaped having a bottom I! and a vertical circular outerwall ll, as best shown in Figure 3. Fins 15 are preferably formed on the outer surface of wall ll to provide greater heat radiating surface therefor. Extending from bottom I! of the casing is an inner semi-circular projection l6 thereof, thus forming a channel 11 bounded by wall 14, bottom it and projection I6 in which the resistance element ii is disposed (Figure 2) as will be more.

fully pointed out hereinafter.

A bushing generally indicated as I! is embedded in bottom I! of the casing provided with a nut-shaped inner portion l9 (Figures 2' and 3) and a threaded extension 20 projecting from the bottom as bat seen in Figure 2. Preferably a lug 2i (Fi u e 2) extends from the bottom of the casing and thus the casing containing the entire rheostat construction may be mounted on a panel 22 with extension 20 extending through a hole in the panel and lug 2| extending into another hole I l thereof. A nut 25 (Figure 2) threaded on extension 20 holds the casing firmly in position on the panel 22. It will be understood, however, that various other expdients could be used in mounting the casing on a panel or other type of support. Preferably panel 22 is metal and thus capable of receiving heat conduction from the casing.

Referring now to Figure 4, resistance element ii comprises a cylindrical shaped metallic core 26 desirably made from some metal having high heat conducting characteristics such as copper or aluminum. The reduced ends 26a and 26b of the core meet to complete the cylindrical shape thereof and have formed therein a hole 2|.

Core 26 is covered throughout its length except for e'nds 26a and 26b. thereof with dielectric material 28, such material being capable of withstanding high temperatures and yet being highly conductive as far as possible. In practice, we have found electrical asbestos or high temperature cement well suited for this purpose.

Resistance wire 29 is wound about core 26 over the dielectric material 28 having its ends soldered or otherwise secured to metal tabs generally indicated at 30 and 3|. Metal tabs 30 and 3| have portions 32 and 33 wrapped about the core over-the material 28 and radially extending projections 34 and 35 for connection in the desired circuit. Wire 29 is held in position by a cementitious coating leaving the uppersurfaces 29a thereof exposed for engagement with the contactor l2.

As best shown in Figure 2, resistance element fits within the channel l1 between wall I4, bottom l3 and projection l6 and is secured in this position by a rivet 36 extending through wall l4 (Figure 2) and hole 21 in the ends 26a and 26b of the core 25. Thus, rivet 36 firmly holds the element in position and more particularly assures a direct contact between the ends 26a and 26b and the metallic casing H) for efficient passage of heat therebetween. To insulate the wire 29 on the resistance element H from the casing I and yet provide for as, much heat transfer as possible therebetween, we prefer to utilize sheet mica. Thus, as shown in Figure 2, between element II and wall |4 there is a mica strip 31 and a similar mica strip 38 is disposed between the element and projection l6. A circular strip of mica 39 rests on bottom 93 beneath the bottom edge of the element so that the element is surrounded on three sides by mica and thus a thorough electrical insulation therebetween is provided; However, mica strips 31, 38 and 39 are thin and thus allow ready heat transfer from the element to the casing ii]. It

will be understood that other types of dielectric material capable of heat conduction could be used with satisfactory results.

A shaft 40 is rotatably mounted in bushing I8, one end thereof being secured to the usual dialing knob 4| (Figure 2) on the outside of the panel. Contactor |2 is-secured to the other end of shaft 40 as best shown in Figures 1 and 2.

Contactor 2 includes a dielectric support generally indicated at 42 and secured to the end of shaft 40 in any desired manner, for example a riveted piece 43. Support 42 includes a projection 44 extending downwardly about the shaft 40 and the contactor arm l2 includes a flat circular piece generally indicated at 45 fitting about projection 44. A U-shaped upright projection of metallic piece 45 fits about a small exten: sion 41 (Figure 1) of support 42. Thus, the contactor arm I2 is supported-in the position shown in Figure 2 and pressed downwardly by a compression spring 48 disposed between the support 42 and the piece 45. contactor I2 is preferably riveted to an upright extension 50 of piece 45. Brush 48 may take any The brush 49 of the casing adjacent an inset therein thus pro-.

viding a support for a dielectric foundation piece generally indicated at 54 (Figures 2 and 3)..

Projections 34 and 35 of taps 30 and 3| extend through channels 55 and 56 in foundation piece.

54. A tap 57 is secured in a channel 58 in the foundation piece by a rivet 59 and extends inwardly to be connected by way of a rivet 60 to a spiral spring 6|. The other end of spiral spring'6I is connected in any suitable manner, f

for example riveting, to a lug 62 extending from piece 45. Thus, tap 57 is connected to contactor l2 and the opposite ends of the wire on element H are connected to taps 30and 3|.

Accordingly, resistance wire 29 on the resistance element is in close proximity to the metallic core 25 forming a part of the resistance element. Furthermore, the core 26 is connected by way of rivet 36 andends 26a and 26b to the casing and the entire base of thr casing restsupon the metal panel 22. The opposite sides of the resistance element are adjacent wall l4 of the casing and projection l6 thereof so that heat generated in the resistance element may pass to these parts of the casing.

26 thereof as Well as by the wall l4 and the projection it throughout the length of the resistance element to effect an even distribution of the heat especially throughout the heated portion of the element, it being understood that only that portion of the element is heated which is in the circuit as determined by the position of contactor i2 on the resistance element. Thus, in Figure 1 approximately one half of the resistance element is in circuit, 1. e. a half between the twelve oclock and five oclock position, and thus this partof the resistance element would be heated, the heat therein being evenly distributed throughout. More important, however, is the fact that heat generated in the resistance element during operation is rapidly conducted away from the resistance element to be dissipated in the atmosphere. Heat passing to the casing by way of ends 26a and 26b as well as the heat passing intowall I4 and projection I6 filters into all portions of the casing as well as the panel 22 to which the casing is connected. Thus, this large metallic surface exposed to the atmosphere dissipates heat rapidly and consequently operation of the rheostat results in a continuous cooling effect, which efiectis utilized to greatly increase the current carrying capacity of the entire construction.

For example, in operation the rheostat maybe cooling characteristics of our rheostat, a much larger current may be carried safely thereby, even where the rheostat is in a circuit necessitating the use of only a fraction of the resistance element as described above.

It will thus be seen that we have provided a thoroughly practical rheostat construction in which the several objects hereinabove referred to as well as many others are successfully accomplished.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth, orshown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In rheostat construction, in combination, a cup-shaped housing formed of material having high thermal conductivity, means forming an annular chamber in said housing, means comprising dielectric material having high thermal conductivity for lining said chamber, a resistance element cylindrical in shape mounted in said chamber concentrically with the vertical wall of the casing, said element including a metallic core connected to said casing, and taps connected to and extending from said element.

2. In rheostat construction, in combination, a

' cup-shaped casing formed of metal having high thermal conductivity, a cylindrical resistance element including a metallic core mounted in said casing adjacent the vertical wall thereof, a thin strip formed of dielectric material having high thermal conductivity sistance element and said vertical Well, said resistance element, said strip and said wall being contiguous, and means forming heat radiating fins on said wall.

3. In rheostat construction, in combination, a

metal cup-shaped casing, a resistance element disposedin heat exchange relationship with a wall of said metal casing, said element compris-" ing a substantially cylindrical metallic core condisposed between said re-- cup-shaped metallic casing,

ing all but a small exposed portion of said wire for holding the turns thereof in ship. I 4

,4. In rheostat construction, in combination, a

an arcuate projection formed integrally with the bottom-of said casing and extending therefrom concentrically with the vertical wall of annularchamber therein, a thin mica lining for said chamber, and a resistance element mounted in said chamber contiguous to said mica lining, said resistance element including a metallic core directly connected to said casing.

5. In rheostat construction, in combination, a cup-shaped metallic casing, a resistance element cylindrical in shape mounted in said casing and concentric with the vertical wall thereof, said spaced relationelement having a metallic core riveted to said casing, and sheet mica disposed between the side and bottom portions of said element and said casing.

6. In rheostat construction, in combination, a cup-shaped metallic casing, a resistance element cylindrical in shape'mounted in said casing and concentric with the vertical wall thereof, said element having a metallic core riveted to said casing, and sheet mica disposed between the side and bottom portions of said element and said casing, said casing having a cylindrical projection adjacent the inner surface of said element.

7. In rheostat construction, in combination, a

cup-shaped metallic casing, a resistance element cylindrical in shape mounted in said casing and concentric with the vertical wall thereof, said element having a metallic core riveted to said casing, sheet mica disposed between the side and bottom portions of said element and said casing, and taps extending radially from the opposite ends of said element.

. ANDREW A. FOLEY.

iEMJL REISMAN.

said casing to form an a 

